Abstract Over a dozen wildfires broke out in the northwest of California on October 8, 2017. Fueled by hot dry conditions and strong winds, the conflagration consumed well over 5000 structures, led to evacuation of 90,000 and killed 42 people. The proposed ?Wildfires & Health ? Assessment of the Toll in NOrthWest California? (WHAT-NOW?) project aims to identify short-term physical and mental health effects in survivors along with their urgent needs; collect environmental samples and blood specimens for assessing chemicals released by combustion of urban structures that may differ from those produced by forest and grassland fires; lay the foundation for understanding long-term impacts; and provide information of direct value to local and statewide health and environmental agencies, non-profits, medical professionals, and the broad public. Two cohorts will be established through an initial survey: a probability sample with in-person interviews of households selected by 2-stage cluster sampling of Census blocks, and a convenience sample generated by major efforts to publicize the online version of the survey through the county health departments, networks of community organizations, the medical community and a coordinated campaign leveraging social and traditional media. Prevalence of short-term respiratory, other physical, and mental health symptoms, and their associations with evacuation status, sociodemographics, losses (home, loved ones, pets, jobs, income) and pre-fire health status will be assessed. To address disparities in fire-related health effects, residents of Census blocks with similar fire damage but different socioeconomic status will be compared. Preliminary analyses of paired air and ash samples collected beginning a few weeks after the fires will identify chemical differences for residential vs. open land. Both overall and county-specific results will be generated. A multi-pronged dissemination strategy will be developed in consultation with local and other stakeholders and dissemination materials will be culturally-relevant and available in at least English and Spanish. This project is a collaboration of the UC Davis Environmental Health Sciences Center, county health departments, and other state and federal agencies and UC Davis centers; it will answer critical questions about the short-term impacts of the urban wildfires on survivors and unique chemical features of the combustion by-products released into the environment, collect time-sensitive samples, and enable follow-up of residents to determine long-term consequences for mental and physical health. The information learned will assist policy-makers and organizations in responding to questions from the public, hastening the recovery and planning for future similar disasters.